U.S. Secretary of State John Kerry spoke with Russian Foreign Minister Sergei Lavrov over the phone Monday about efforts to facilitate an immediate cease-fire in the escalated Nagorno-Karabakh conflict.
"Topic number one was to discuss efforts to secure an immediate end of the violence that has erupted along the Nagorno-Karabakh line of conflict," said State Department deputy spokesman Mark Toner.
Toner said the U.S. encouraged Armenia and Azerbaijan to resume settlement talks, and to avoid further escalation.
The mountainous region of Nagorno-Karabakh has been the subject of a long-lasting dispute between regional rivals Armenia and Azerbaijan. While it lies within the territory of Azerbaijan, it has been under the control of local ethnic Armenian forces and the Armenian military since the end of a war in 1994.
Azerbaijan says three of its soldiers were killed as fighting raged for a third day over the separatist region, with Armenia warning the situation could escalate into a full-scale war.
The Associated Press cites Azerbaijani Defense Ministry spokesman Vagif Dargyakhly as saying rebels were shelling Azerbaijani military positions and front-line villages, despite the government's announcement Sunday of a unilateral cease-fire.
Remains of a downed Azerbaijani forces helicopter lie in a field in the separatist Nagorno-Karabakh region, April 2, 2016.
Armenian President Serzh Sargsyan accused Azerbaijan of continuing "offensive, provocative acts" which he says are targeting civilian areas. "Since the so-called 'unilateral truce' was announced, Azerbaijan's artillery has continued working in the direction of the populated areas of Karabakh," Sargsyan was quoted saying at a meeting of the Organization for Security and Cooperation in Europe.
He warned that his country could formalize its ties with Nagorno-Karabakh by officially recognizing its independence if the fighting escalates.
The unilateral cease-fire was declared a day after clashes between the two sides left 30 soldiers dead.
The two sides are separated by a demilitarized buffer zone, but each side accuses the other of numerous violations.
Last week, Kerry told visiting Azerbaijani President Ilham Aliyev that the U.S. wants to see "an ultimate resolution of the frozen conflict of Nagorno-Karabakh that needs to be a negotiated settlement and something that has to be worked on over time."